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<html>
<head>
	<meta charset="utf-8">
	<title></title>
	<script type="text/javascript">
		// indexOf():返回数组中给定的一个元素的第一次出现的索引，如果找不到返回-1
		// lastIndexOf()

		// includes():判断数组中是否包含一个元素，true/false

		var arr = ['hello','js',true,30,10,20,undefined,null,30,40,'哈哈','JS'];
		console.log(arr.indexOf(50));
		console.log(arr.lastIndexOf(30));

		console.log(arr.includes(78));
		console.log(arr.includes(20));
	</script>
</head>
<body>

</body>
</html>